Thermodynamic Properties of the Ion-Channels in the Nerve-Membrane
The cell membrane is normally required to accomplish many different transport functions at the same time. There is now abundant evidence that most of these activities employ a relatively low density of physically distinct and non-interacting pathways, provided by specific proteins embedded in a common lipid matrix and structured as hydrophylic pores which open or close as a result of conformational fluctuations modulated by the membrane environment. Most experiments supporting the above notion have been performed on electrically excitable membranes where voltage-gated ion-channels provide the simplest molecular interpretation of the classic HODGKIN-HUXLEY mathematical description of nervous conduction . However, hydrophylic pores are likely to be a general type of structure for the transport of water-soluble compounds across a biological membrane. There is evidence, indeed, that porous structures underlie the passive transport of ions and non-electrolytes between contacting cells  and between individual cells and their environment . The experiments demonstrating the discrete nature of nerve membrane permeabilities are those which provide estimates of channel densities and/or of the electrical conductance of a single open channel. Four different experimental approaches have been used: binding studies, gating current measurements, currents fluctuation analysis, and single channel recordings.
KeywordsSodium Channel Channel State Single Channel Closed State Potassium Current
Unable to display preview. Download preview PDF.
- J.A. TALVESHEIMO, M.M. TAMKUN and W.A, CATTERALL, J. Biol. Chem., 257, 11868 (1982).Google Scholar
- W. ALMERS, Rev. Physiol. Biochem. Pharmacol., 82, 97 (1978).Google Scholar
- J.S. BENDAT and A.G. PIERSOL, Random Data: Analysis and Measurement Procedures, Wiley, New York (1971).Google Scholar
- F. CONTI, Current Topics in Membranes and Transport, 22, 371 (1984).Google Scholar
- T.L. HILL, An Introduction to Statistical Thermodynamics, Addison-Wesley, Reading, Mass. (1960).Google Scholar
- S. GLASSTONE, K.J. LAIDLER and H. EYRING, The Theory of Rate Processes, McGraw-Hill, New York (1941).Google Scholar